Mr Swinney said the study would look at how RET could be tested on a route, or routes, to the isles.

He said: "I believe that the way forward is to consider the benefits of introducing a road equivalent tariff (RET) approach to setting fares in Scotland.

"This approach would not just benefit islanders by providing cheaper fares but could also boost island economies by attracting tourists and supporting businesses."

Transport body Highlands and Islands Transport Partnership in Scotland (Hitrans) has previously estimated that 700 jobs and £22m a year could be generated by reducing ferry fares to the Western Isles by 30%.

In May last year, the previous Scottish Executive introduced cheaper air fares for people living in parts of the Highlands and Islands.

The 40% discount scheme, costing an estimated £11m a year, applies to trips to Scotland's main airports.

FARES FACTFILE

The scheme could slash the cost of a return ticket between Ullapool and Stornoway from £200 to £30

The first phase of the study will review approaches to fare setting for public service ferries in other countries, including the RET approach

The study will run this year and a pilot scheme is expected to be launched early next year

Discounts are available to passengers living in the Northern and Western Isles and those in Islay, Jura and Caithness.

Alf Baird, a professor of maritime transport, said cheaper travel by sea was welcome but added there should be a move away from state-owned services.